Filter devices of this type are widely used for filtration of a wide variety of technical fluids, for example, for hydraulic fluids, cooling lubricants, fuels, lubricating oils and the like. Since operational disruptions or malfunctions of such filter devices may result in the damage to or the destruction of systems downstream, which disruptions or malfunctions may cause economic damage, great importance is attached to the operational reliability of the particular filter device. For this reason, continuous efforts are made in the industry toward improving the operating characteristics and avoiding potential trouble sources. The maintenance work periodically carried out during the operation of the filter devices constitutes a potential trouble source with potentially serious consequences. As well known, filter elements, following certain periods of operation, when sensor devices detect a rise in differential pressure that signals a corresponding contaminant load in the filter element, must be removed as worn and replaced by a new filter element.
To avoid operating errors in connection with a filter element replacement, a filter device of this type is already known from WO 2006/012031 A1, where the device is inoperable if, through an oversight, no filter element is installed in its functional position within the filter housing. The known solution in this case provides a valve device, the closing body of which, in a closed position, blocks the discharge flow of filtrate from the filter housing, and which is fixed in the closed position by a locking device. To release the closing body and, therefore, to unblock the discharge path of the filtrate, the locking device may be moved from the locking position into an inoperative unlocking position. To effect unlocking, a control element is provided on the filter element to be installed in the filter housing, which control element acts to mechanically unblock the locking device during the course of the installation procedure. This arrangement ensures that the discharge flow of filtrate is possible only with a filter element that is installed in the functional position. In the event the device is put into operation when the filter element is inadvertently not installed, the closing body of the valve device remains locked in the closed position, so that the pressure sensor device detects a corresponding rise in pressure to then signal a maintenance error.
The valve device and the locking device in the known solution are provided on a disk extending in a plane in the housing head perpendicular to the main axis. An elevation in the form of a cylindrical sleeve is provided concentrically to the main axis on the upper side of the disk facing away from the housing pot. The upper open end of the elevation forms the flow-through opening for filtrate. The filtrate flows from the inner filtrate chamber of an associated filter element via a connecting piece situated at its end cap.
In the installed functional position of the filter element, the connecting piece extends into the sleeve body. The closing body of the valve device is a round valve plate that, in the closed position, forms, as a valve seat, a seal at the edge of the flow-through opening of the sleeve body when acted upon by a pretension spring, and blocks the exit flow of filtrate.
The locking device, as shown in FIGS. 10 and 15 of WO 2006/012031 A1, includes two blocking members, each in the form of a slide member. The blocking members may be moved in radial directions toward one another and away from one another on the disk by slide tracks arranged diametrically opposite one another on both sides of the sleeve body. Each slide member includes a radially, inward projecting locking part that, in the radially, inwardly slid locking position, overlaps, and thereby locks, the valve plate situated in the closed position. In addition, each slide member includes an actuating part extending below the flow-through opening into the sleeve body that, at its free end, forms a control surface extending diagonally to the main axis. Both slide members are pretensioned by a spring assembly into the locking position close to one another. In order to move the locking device into the unlocking position, i.e., to move the slide members radially apart in the slide tracks, projecting tabs with cam surfaces on the ends thereof are provided as control parts on an axially projecting connecting piece on the end cap of each filter element to be installed. In the functional position, the connecting piece protrudes into the sleeve body of the disk, the angular surfaces of which rest as cam surfaces against the actuating part of the slide members when the tabs in the sleeve body move axially during the course of installation. The cam surfaces on the tabs push the control surfaces on the actuating part of the slide members radially outward to disengage the locking parts of the slide members from the valve plate.
The known solution has definite disadvantages. When converting the axial movement to the radial movements of the slide members occurring against the spring force, as these take place as a result of the interaction of the cam surface on the end cap of the filter element with the control surfaces of the slide members, high actuating forces are required. These forces result in correspondingly high local surface pressures, making it necessary to construct slide member guides that are complex in design in order to keep the friction forces that result from the lateral forces occurring during the interaction of the cam surfaces with the control surfaces on the slide members within limits. This circumstance also requires minimizing the spring force that pre-tensions the slide members in the locking position. Thus, on the whole, the operational reliability of the valve and locking device of the known solution leaves room for improvement.
A further disadvantage are the sealing problems existing between the slide member guides and the filtrate-guiding sleeve body, because the actuating parts of the slide members extend out of the slide member guides into the sleeve body. Another disadvantage is that the selection of material for relevant functional elements is limited due to the high material stresses. Given the mechanical stress of the tabs functioning as control parts, special materials must be used, such as metals or special high-strength plastics. The same applies to the slide members and slide member guides and to the associated disk in the filter head.